Cancer is the second leading course for all deaths in the United States, surpassed only slightly by heart disease. Although down-regulation of gene expression by siRNA has been shown to be both potent and target gene-specific, there is currently no therapeutically acceptable method for siRNA delivery that targets only cancer cells with high efficiency without affecting normal cells. In the proposed research, we will prepare, characterize, and test a novel folate-conjugated multicomponent gold-siRNA nanoplex system, which permits cancer cell-specific delivery of the nanoplexes through folate receptor-assisted endocytosis. The gold-siRNA nanoplex will be assembled stepwise from pre-made gold nanoparticles and chemically and enzymatically synthesized thioRNA and thioRNA-PEG-folate conjugates. Extensive characterization will be performed by NMR, HPLC, gel electrophoresis, dynamic light scattering, zeta potential, and transmission electron microscopy. Using different cancer cell lines (A549, KB, HeLa, and SKOV3), we will analyze intracellular delivery efficiency, specific gene knockdown, and cellular function studies including inhibition of cell growth and cell death. It is expected that the proposed research will develop a new siRNA delivery system based on actively targeted gold nanoparticles. Effective down-regulation of essential genes [survivin and CASP8AP2 (caspase 8 associated protein 2, an apoptosis factor)] will lead to inhibition of cancer cell growth and cancer cell death. PUBLIC HEALTH RELEVANCE: The proposed project will develop a novel folate-conjugated Au-siRNA nanoplex system. Specific siRNA delivery to cancer cells and efficient down-regulation of gene expression will be achieved by the Au-siRNA nanoplex. Knockdown of essential genes will cause cancer cell growth inhibition and cancer cell death. The research may lead to the development of therapeutic siRNA delivery systems for cancer treatment.